Hydraulic pump system



2,987,003 HYDRAULIC PUMP SYSTEM James H. Kress, Waterloo, Iowa,assignor, by mesne assignments, to Deere & Company, a corporation ofDelaware 1 Filed Jan. 8, 1958, Ser. No. 707,816

7 Claims. (Cl. 103-38) I United States Patent This invention relates toa hydraulic pump system and strokes, and pilot pressure taken off thesystem in'g'eneral is used to oppose the bias and thereby to reduce thestrokes and consequently to reduce the output. In other types of pumps,the pistons are moved forcibly on their discharge strokes and arereturned on their intake strokes by relatively strong springs. Oneinherent disadvantage of that type of pump is that during lowtemperature operation, the pumping pistons may cling to their cylinderwalls as a result of high viscosity of the fluid. Accord ing to thepresent invention, these and other disadvantages are overcome by meansfor positively returning the pistons on their full intake strokes or anyincrement thereof independent of oil viscosity and related factors. Thisfeature is embodied in an improved pump in which theoperationalcharacteristics of the pump are such as to impose on thepistons a bias tending to retain them at Y the outer ends of theirdischarge strokes, plus fluid means operative to vary the extent towhich this inherent bias is overcome and thereby to vary the extent towhich the pistons will return on their intake strokes, thus enablingvariation in'pumpoutput from no-stroke 'to full-stroke. Another featureof the invention is to utilize relatively light return springs operativeonly in primingthe pump and having no efiect on control of the strokeregulation;

It is another object of the invention to provide an improved pumpinwhich pilot pistonsare respectively coaxial with pumping pistons, andfluid manifold means is provided for interconnecting the pilot cylindersfor sup-.

plying fluid thereto. A significant feature of the invention resides inaregulating valve for automatically varying the volume inthe manifold inpilot cylinders in accordance with load requirements on whatever deviceis connectedto the pump.

The foregoing and other important objects and desirable featuresinherent in and encompassed by the invention'will become apparent tothose versed in the art as a preferred embodiment of theinvention isdisclosed, by Way ofcXample, in the single figure in the accompanyingdrawings and appended description.

The variable-displacement pump is indicated in its entirety by thenumeral 10 and comprises means affording to drive an eccentric 16. Thepump further includes a plurality of pump cylinders 18 disposed'radiallyas re- 14 and respectively ing valve to besubsequently described.However, this a crank case 12 in which acrank shaft 14 is operative Lthe like. ln'such systems, biasing means normally acts to increase thepump output by increasing the piston memo:

pistons are appropriately manifolde'd for connection to the line 24, in,a manner that will beobvious from the drawing without furtherdescription.

One of the pistons is shown in section so as to disclose the interiorcomponents thereof. From, this illustration it will be seen that theinner end of the piston has an in: take port 26 in communication withthe crank case 12 and normally closed by a ball 28 under action of arelatively lightconical spring 30. As the top piston moves down on itsintake stroke, the ball 28 lifts from the port 26, and fluid is takeninto the interior of the piston for discharge via a discharge port 32when the piston moves upwardly or outwardly on its discharge stroke. The

discharge port is controlled by a ball 34 spring loaded The outer ordischarge end of each cylinder 18. is

' closed, as by athreaded plug 38, and this plug is hollow to afford apilot chamber or cylinder 40. In the preferred construction illustrated,the pilot cylinder 40 is coaxial with the respective pump cylinder 18. Apilot piston 42-is reciprocable in the pilot cylinder 40 and ismechanically connected to theinterior of the pumping.

piston 20 as by an enlarged head 44 and snap ring 46. The head 44 isslotted at to enable fluidto pass from the intake port 26 to thedischarge port 32 A relatively light spring 50 acts between the 'plug 38and the pump'." v piston20 andnormally urges the pump piston-radiallyinwardly. However, this spring,. as. already stated, is relatively lightand is instrumental primarily as means for facilitating the priming ofthe pump. This spring could be dispensed with if the arrangementinvolves a" reservoir'oil level higher than the pump and the regulatqdetail. is of minor importance in the present disclosure.

Sufii'ce it to notethat the pump and pilot pistons 20 and 42 move inunison. The same construction is involved in the other two pistonassemblies illustrated. The outer or upper end of the plug 38 isdrilled'at 52 so that the pilot pistonsmay be connected by a manifold54.

In the representative'system shown, the high pressure line 24 isconnected to the inlet side 56 of a closed center control valve 58 whichhas a pair of motor ports 60 and 62 connected respectively to oppositeendsofafluid in the regulating valve housing 74 carries a valve mem ber86 biased to a closed position by a spring 88 which is adjustable at 90.When the valve is in its closed posi- I tion, the ports 76, 78, and areisolated from each other.

The port 76 is 'connectedto the high pressure line bya control lineportion 92 and the outlet port 78 is connectcd to the manifold by acommunicating control line portion 94. The end of the regulating valvebore 84 opposite to the spring 88 affords a chamber 96 which isconnected by a line 98 to the-high pressure line 24 upstream of thecontrol valve 58.

The arrangement is such that when pressure in the line 24 is at apredetermined value, the valve 86 is hal anccd between this pressure andthe spring 88. to incur the closed position shown in the drawing,whereby the olume of fluid in the manifold 5'4 is constant. Thus,althoughjthe pilot pistons 42 move with the pump pistons 28 and have apumping action, the fluid in'the manifold merely circulates from onepilot cylinder 40 to the other.

Whenthe'control valve 58 is in neutral, as shown, the 7 pressure in theline 24 is that predetermined by'the spring 88, and the pistons 20 arereciprocated on strokes Patented Juno 6,'i961 will overcome fluidpressure in the line 98 and chamber 96 and thevalve member 86 will moveto the right,,in-

terconnecting ports 76 and 78 and thus supplying fluid from the highpressureline 24 to the manifold 54 via 9Z-76--7894. This fluid will ofcourse enter the pilot cylinders 40 and will increase the stroke of eachpiston 20 for the following reason: during operation of the pump,rotation is so rapid that the pistons 20 tend to stay out to theirdischarge ends and consequently fail to completely return on theirintake strokes. -Thus, their effective strokes are, shorter than theirpredeterminedmaximum strokes. If this condition persists, and theregulating valve member 86'is in its closed position as shown, thevolume of fluid in the manifold 54 and pilot chambers or cylinders '40is constant, and the intake stroke cannot be increased. Thus, thevolumetric output.

of the-pump will depend upon the extent to which the pumping pistons 20return on their intake strokes.

In the example just assumed, with the pressure drop in the line 24because of opening of the control valve 58, fluid from the line 24 issupplied to the manifold 54 and thus forces the pistons further on theirintake strokes, which consequently means an increase in their dischargestrokes as well, thereby increasing the volumetric output. The pressurein the line 24 depends of course upon-the load encountered by the motor64, and when this pressure increases enough to overcome the spring 88,the regulating valve member 86will return to neutral and will maintainthe constant volume of fluid in the manifold 54 and pilot cylinders 40as long as the volumetric requirement remains unchanged. -If therequirement increases, the valve member 86 will again shift to the rightand add fluid. In the event that the line 24 achieves an instantaneouspressure rise, as by the motor 64 reaching the end of its stroke orencountering an obstacle that it cannot overcome, pressure rise in theregu- 'lating valve chamber 96 will cause the valve member 86 to shiftto the left, thus interconnecting ports 78 and 80, whereby fluid will besubtracted from the manifold and pilot cylinder volume via94--78-:8082.'

The valve bore 84 is connected behind the valve member 86 to reservoirby a drain line 100 for accepting leakage past this valve member.

In short, and assuming a stabilized pump running condition, whereinfluid viscosityand pump'speed are considered constant, 'an increase inpump stroke follows decrease of line pressure in line 24, which ofcourse entails decrease in pressure acting via the line 98 on the righthand end .of the valve member 86 in the chamber 96. Likewise, a decreasein pump stroke follows an increase in the pilot pressure inthe chamber96 as a result of a decrease in line pressure. For any constantvolumetric output, the total quantity of fluid remains approximatelyconstant in the pilot manifold 54 and pilot cylinders 40, since thepilot fluid circulates from one pilot cylinder to another. If anexternal cont-rolmeans, such as the control valve 58, incurs a situationin which more oil flows into the pilot manifold line, the pilot pistons,which act integrally-with the pump pistons 20, must move toward thecenter of the pump, consequently forcibly moving the pump pistons 20 ontheir intake strokes so that the output of the pump isincreased.

From the foregoing, it will be'seen that the pump construction itself iscompact and simple, and in a preferred embodiment the pilot cylindersand pistons are respectively coaxial with the pump cylinders andpistons. The regulating valve 72 affords means forautomatic regulationof the volume of fluid in the pilot manifold, and

this regulating valve controls pump displacement according to volumetricrequirements of the hydraulic motor 64, for example. Other features notcategorically enumerated will readily occur to those versed in the art,as will many modifications and alterations in the preferred embodimentdisclosed, all of which may be achieved without departure-from thespirit and scope of the invention.

What is claimed is:

1. A hydraulic system, comprising: a variable-die placement pump havinga discharge line and further having a plurality of consecutivelyreciprocable pumping elements for pressurizing said line, each elementbeing movable on intake and discharge strokes of predotermined lengthand conditioned by forces during operation to tend toward the end of itsdischarge stroke whereby the length of the intake stroke is less thansaid predetermined length; means connected to the pump and providing aplurality of fluid chambers, one for each element; a plurality ofpistons, one in each chamber and connected to and movable with thepumping element in that chamber; a fluid manifold interconncctdecreasein the volumetric requirements imposed on the ment pump having adischarge line and further having a plurality'of pump cylinders and aplurality of consecutively reciprocable pump pistons respectively insaid cylinders for pressurizing said line, each pump piston beingmovable on intake and discharge strokes of predetermined length andconditioned by forces during operation to tend toward the end of thedischarge stroke whereby the length of the intake stroke is less thansaid predetermined length; means connected to the pump and providingingaplurality of pilot cylinders, one coaxial with and at the discharge endof each' pump cylinder; a pluralityof pilot pistons, one in eachpilotcylinder and connected to and movable with the associated pumppiston; a fluid manifold interconnecting the pilot cylinders; supplymeans connected between the discharge line and manifold for supplyingfluid to the pilot cylinders viathe manifold in opposition to theaforesaid condition to increase the return of the pump pistons on theirintake strokes; and means connected to and operative on the supply meansin response to variations in the volumetric requirements imposed on thedischarge line to vary the amount of fluid in said manifold and pilotcylinders and thus to incur intake strokes of the elements respectivelyaccording to increase and decrease in the volumetric requirementsimposed on the discharge line.

3. A hydraulic system, comprising: a variable-displacement pump having aplurality of consecutively reciprocable pumping elements, each movableon intake and exhaust strokes of predetermined lengthand conditioned byforces during operation to tend toward the end of the discharge strokewhereby the length of the intake stroke is less than said predeterminedlength; a high-pressure line connected to the discharge side of saidpumping elements; means connected to the pump and providing a pluralityof fluid chambers, one for each element; a plurality of pistons, one ineach chamber and connected to and movable with the associated pumpingelement; a fluid manifold interconnecting the chambers; a control lineconnected to the high-pressure line and to the manifold for supplyingfluid to the chambers via said manifold to move the pistons and therebyto return the elements forcibly on their intake strokes in opposition tothe aforesaid condition; and a regulating valve in said control linehaving open and closed positions respectively opening and blocking saidcontrol line and including a piston portion open to the high-pressureline, said regulating valve being operative toincur its'closed positionin response to a predetermined pressure in said high-pressure line so asto maintain a constant predetermined fluid volume in the manifold andchambers and to incur its open position in response to a decreaseinpressure in said high-pressure line'to add fluid to said manifold andchambers.

4. The invention defined in claim 3, in which: the regulating valve hasa dump position achievable in response to a predetermined increase inpressure in the high-pressure line to dump fluid from the manifold andchambers.

5. A hydraulic system, comprising: a variable-displacement pump having adischarge line and further having a plurality of consecutivelyreciprocable pumping elements for pressurizing said line, each elementbeing movable on intake and exhaust strokes of predetermined length andconditioned by forces during operation to tend toward the end of thedischarge stroke whereby the length of the intake stroke is less thansaid predetermined length; means connected to the pump and providing aplurality of fluid chambers, one for each element; a plurality ofpistons, one in each chamber and connected to and movable with theassociated pumping element; a fluid manifold interconnecting thechambers; a control line interconnecting the discharge line and manifoldfor supplying fluid to the chambers via said manifold to move thepistons and thereby to return the elements forcibly on their intakestrokes in opposition to the aforesaid condition; a regulating valve insaid control line having open and closed positions respectively openingand blocking said control line and including a fluid-receivable portioncommunicating with the discharge line, said regulating valve beingoperative to incur its closed position in response to a predeterminedpressure in said discharge line so as to maintain a constantpredetermined fluid volume in the manifold and chambers and to incur itsopen position in response to a decrease in pressure in said dis chargeline to add fluid to said manifold and chambers! 6. The inventiondefined in claim 5, in which: the regulating valve has a dump positionachievable in response to a predetermined increase in pressure in thedischarge line to dump fluid from the manifold and chambers.

7. A hydraulic system, comprising: a variable displacement pump having aplurality of consecutively reciprocable pumping elements, each movableon intake and discharge strokes of predetermined length and conditionedby forces during operation to tend toward the end'of its dischargestroke whereby the length of the intake stroke is less than saidpredetermined length; means connected to the pump and providing aplurality of fluid chambers, one for each element;a plurality'ofpistons, one in each chamber and connected to and movable with thepumping element in that chamber; a fluid manifold interconnecting thechambers; supply means connected between the discharge side of the pumpand manifold for supplying fluid to the chambers via said manifold tomove the pistons and thereby to return the elements forcibly on theirintake strokes in opposition to theaforesaid condition; and meansconnected to and," operative on the supply means for varying the amountof fluid in said manifold and chambers and thus to vary the extent towhich the elements are returned on their intake strokes.

References Cited in the file of this patent UNITED STATES PATENTS

